Freezing seeds

[markcond]

This is more out of interest than anything. I was wondering if seeds of the following plants could survive freezing for long periods : Acacia Maidenii etc, Cacti, HBWR, Ipomoea species. I was imagining the day when I have to many seeds

[occidentalis]

This is more out of interest than anything. I was wondering if seeds of the following plants could survive freezing for long periods : Acacia Maidenii etc, Cacti, HBWR, Ipomoea species. I was imagining the day when I have to many seeds

Long term storage of seeds is generally carried out by freezing. However, you have to dry them out first. Standard technique is to keep them at 15 ºC and 15% RH for a few weeks, and then freeze them at -20 ºC. Obviously they need to be frozen in an atmosphere of that humidity, so you need to bag them up in fairly dry air in a sealed bag. This works for most species. There are some that don't like this, known as recalcitrant seeds. And there are various other methods for different recalcitrant seeds, but generally they are just put in the too hard basket. As for your species of interest, I don't know whether they are recalcitrant or orthodox except for the Acacia which should be fine. Do a test germination with as many seeds as you can (up to 100), then after 1 year of storage do another test, then another every 2 years after that. That way you will pick up if they start to decline in viability. That means you have to plan ahead when you store them and keep them in separate bags so it is easy to test a sub sample without opening the main bag.

[markcond]

Thanks mate, your post answered quite a few question that I had. Do you know how the cacti seeds would cope with freezing,

Cheers'

markcond

[Vertmorpheus]

A little faith goes a long way, too If you need them, they will come... even if you're a bitter grey haired muppet like me.

Freezing of plant matter depends on speed, which dictates size of ice crystals formed internall... small enough, being fast enough, and the ice forms around and between cells... too slow, comes out chunky, ruptures cells which upon defrosting go mushy.

Dryness would help with moisture content (low moisture and a fast freeze would give very low levels of very fine crystals internally, minimal damage) but some species, the closer you get to "shelf dry" the less viable they are, by nature... in which case fiddling around with freezing would just be another lil stress for them to overcome at some stage. I know tiny dry herb seeds react ok to freezing (basil, mint, thyme etc) but I have a suspicion the bigger the seeds got, the more drying right out would fuck up their chances... pumpkin seeds etc would be very hard to snap freeze by ice water and deep freeze methods, in comparison to some kind of sage, for example...surface area relative to interior, and all that.

I find the best way to ensure tomorrow's seeds, is to plant today's. Or at least plant last year's before they go festy.

VM

edit... salt.... maybe if you plan to freeze fresh seed, make a point of keeping salinity and salt based ferts reduced before harvest... higher salt content would slow freezing, maybe only by a pinch, but if you're talking numbers games...

further edit... I know that maiden wattles drop seed in areas where ground temps get below freezing, and other wattles with similar sized seeds sprout after winters as bad as -12 ground temps (in heavy clay areas, chilled to the bones of the earth) so they should be ok. Maybe.

Edited December 13, 2008 by Vertmorpheus

[markcond]

Thanks Vert, again some good advice and info.

[Vertmorpheus]

I can't see big fleshy tropicals standing up to a freeze so well though, I think I'd stick with gentle harvest and drying, then stable cool storage... allow them some extra soak time/watering in time one day when you do end up planting them.

Still, if you have the beans to run the tests, I am sure many of us would be grateful to hear the results!

VM

[markcond]

Thanks again Vert, I'll do just that. I'll keep about ten seeds of each my existing seed bank where possible.I have heaps of some seed and only a few of others. I think I mainly want to find out about cacti and HBWR. I'm just wondering if freezing may protect the active compounds (LSA etc). Though I don't know about the stability in non frozen conditions in the first place. I suppose there's something about it in the forum.

Cheers again

Markcond

[Teotzlcoatl]

Steven Brack at Mesa Gardens says Lophophora seeds can be frozen in liquid nitrogen (-346°F) and still be usable.

I was like Whaaaaa?

But he said it was true!

[markcond]

Steven Brack at Mesa Gardens says Lophophora seeds can be frozen in liquid nitrogen (-346°F) and still be usable.

I was like Whaaaaa?

But he said it was true!

Yeah T, I can believe it. I seem to remember hearing/reading that when Liquid Nitrogen is used it freezes so quickly that only small ice crystals can form . Same sort of thing applies to metal. Molten metal when cooled quickly forms small crystals whilst slow cooling results in larger. Take this with a grain of salt as it is ages since I studied this stuff

Cheers T

[Chiral]

Why freeze when u can plant them, sell them or trade them...seems like a risk..and why risk such a seed that's so highly in demand. Leave Walt in the freezer and spread those loph seeds around in the garden or with friends.

H.

[markcond]

Why freeze when u can plant them, sell them or trade them...seems like a risk..and why risk such a seed that's so highly in demand. Leave Walt in the freezer and spread those loph seeds around in the garden or with friends.

H.

I did say it was more out of interest than anything. I'm also thinking along the line of preserving active components contained in seed.

[kadakuda]

the question is more "Can they be dried". if they can handle true *drying* than they are likely able to be frozen. cacti seeds are ok, acacia i have never played with and ipomoea are ok when dry.

some seeds just cant dry, and will be dead when done (many tropical plants, especially fruits). cacti, for the most part...any speice i have tried) can eb dried fully (10%-) and be ok, and they are ok in cold temps.

[markcond]

the question is more "Can they be dried". if they can handle true *drying* than they are likely able to be frozen. cacti seeds are ok, acacia i have never played with and ipomoea are ok when dry.

some seeds just cant dry, and will be dead when done (many tropical plants, especially fruits). cacti, for the most part...any speice i have tried) can eb dried fully (10%-) and be ok, and they are ok in cold temps.

Yeah K. I figure you're right. And I hazard to guess, of the seeds that can be dried, many actually retain some sort of moisture or oil, relying on a impermeable shell or skin of some sort (husk?). If you take a well dried acacia seed and cut it open, the inside is sort of waxy, not brittle dry. But what do I know? I'm only a human....er..I think.

[kadakuda]

many seed banks aim fur under 10% moisture....i dont think 100% dry help anything, but i could be wrong. fan drying and using desiccant seems good enough for most when freezing/fridge storage is used.